Image receiving elements comprising stannic oxide polymers having noble metals reduced thereon

ABSTRACT

Novel image-receiving elements for obtaining photographic images in silver which comprise a support carrying, as a silver precipitating layer, a layer of inorganic stannic oxide polymer (tin hydrosol) having a noble metal reduced thereon.

BACKGROUND OF THE INVENTION

Procedures for preparing photographic images in silver by diffusiontransfer principles are well known in the art. For the formation of thepositive silver images, a latent image contained in an exposedphotosensitive silver halide emulsion is developed and almostconcurrently therewith, a soluble silver complex is obtained by reactionof a silver halide solvent with the unexposed and undeveloped silverhalide of said emulsion. Preferably, the photosensitive silver halideemulsion is developed with a processing composition in a viscouscondition which is spread between the photosensitive element comprisingthe silver halide emulsion and a print-receiving element comprising asuitable silver precipitating layer. The processing composition effectsdevelopment of the latent image in the emulsion and, substantiallycontemporaneously therewith, forms a soluble silver complex, forexample, a thiosulfate or thiocyanate, with undeveloped silver halide.This soluble silver complex is, at least in part, transported in thedirection of the print-receiving element and the silver thereof isprecipitated in the silver precipitating element to form a positiveimage thereon. Procedures of this description are disclosed, forexample, in U.S. Pat. No. 2,543,181 issued to Edwin H. Land. See, also,Edwin H. Land, One Step photography Photographic Journal, Section A, pp.7-15, January 1950.

Additive color reproduction may be produced by exposing a photosensitivesilver halide emulsion through an additive color screen having filtermedia or screen elements each of an individual additive color, such asred or green or blue, and by viewing the reversed or positive silverimage formed by transfer to a transparent print-receiving elementthrough the same or a similar screen which is suitably registered withthe reversed positive image carried by the print-receiving layer.

As examples of suitable film structures for employment in additive colorphotography, mention may be made of U.S. Pat. Nos. 2,861,885; 2,726,154;2,944,894; 3,536,488; 3,615,427; 3,615,428; 3,615,429; 3,615,426, and3,894,871.

In general, silver precipitating nuclei comprise a specific class ofadjuncts well known in the art as adapted to effect catalytic reductionof solubilized silver halide specifically including heavy metals andheavy metal compounds such as the metals of Groups IB, IIB, IVA, VIA andVIII and the reaction products of Groups IB, IIB, IVA and VIII metalswith elements of Group VIA, and my be effectively employed in theconventional concentrations traditionally employed in the art.

Widely used as silver precipitating agents are those disclosed in U.S.Pat. No. 2,698,237 and specifically the metallic sulfides and selenides,there detailed, there terms being understood to include theselenosulfides, the polysulfides, and the polyselenides. For bestresults it is preferred to employ sulfides whose solubility products inan aqueous medium at approximately 20° C. vary between 10⁻ ²³ and 10⁻⁴⁹, and especially the salts of zinc. Also particularly suitable asprecipitating agents are heavy metals such as silver, gold, platinum,palladium, etc., and in this category the noble metals illustrated arepreferred and are generally provided in a matrix as colloidal particles.

SUMMARY OF THE INVENTION

The present invention is directed to a novel image-receiving element forobtaining images in silver, which comprises a support carrying as asilver precipitating layer a layer of an inorganic polymer in whichstannic oxide monomeric units comprise the principal repeating units andwhich further contain metallic monomeric units having a valence of +2having a noble metal reduced thereon. More specifically, the silverprecipitating layer comprises the reaction product of a stannic/stannousoxide polymer and a palladous salt.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an electron micrograph at 100,000 magnification showing thenovel silver precipitating nuclei of the present invention;

FIG. 2 is an electron micrograph at 100,000 magnification showinganother embodiment of the present invention;

FIG. 3 is the same as FIG. 2 except at 300,000 magnification;

FIG. 4 is a spectral transmission curve for a silver image deposited onthe novel image-receiving element of the present invention;

FIG. 5 is a characteristic curve of a silver transfer image in areceiving element of the present invention prepared by plotting theneutral column transmission density to red, green and blue light as afunction of exposure of the silver halide emulsion;

FIG. 6 is an electron micrograph of a cross-section of an unprocessedimage-receiving element of the present invention;

FIG. 7 is an electron micrograph of the image-receiving element of FIG.6 after processing;

FIG. 8 is an electron micrograph of a top view of the image-receivingelement of FIG. 7;

FIG. 9 is an electron micrograph of a cross-section of a prior artunprocessed image-receiving element;

FIG. 10 is an electron micrograph of the image-receiving element of FIG.9 after processing; and

FIG. 11 is an electron micrograph of a top view of the image-receivingelement of FIG. 10.

DETAILED DESCRIPTION OF THE INVENTION

The novel image-receiving element of the present invention comprises asupport having a uniform layer of an inorganic stannic oxide polymerthereon with noble metal nucleating sites deposited on said polymer byin situ reduction of a noble metal salt or complex. When employed in asilver diffusion transfer photographic process, image silver deposits onthe thus-formed noble metal nuclei. While noble metals, such as gold,platinum and palladium, are known in the art as silver nucleatingmaterials, generally they are disposed in an organic polymeric matrix orvacuum deposited on a substrate. In the present invention, it is notnecessary to employ a binder or matrix material to retain the nucleatingsites or to employ the difficult procedures and apparatus involved invacuum deposition. However, if desired, a conventional matrix may beemployed.

It has been found that by employing the receiving layer of the presentinvention, more blue-black tone and better color discrimination can beachieved in the described additive color film units. In addition, moredense packing of the positive silver is obtained and more versatilitywith respect to the employment of other materials in the film unit ispossible.

The desirability of providing diffusion transfer additive color filmunits which provide a positive silver image of high maximum density anda negative silver image or relatively low maximum density has beenrecognized in the prior art (see, for example, U.S. Pat. Nos. 2,861,885;3,536,488 and 3,894,871). The indicated patents as well as others setforth above, disclose a positive transfer image and a negative transferimage, the two images being in separate layers on a common, transparentsupport and viewed as a single positive image. Such positive images maybe referred to for convenience as "integral positive-negative images" oras "integral positive-negative transparencies." The silver precipitatinglayers of the present invention is particularly suitable for use in suchintegral structures.

A class of inorganic polymers is known in which stannic oxide monomericunits are the principal repeating units and which further containsmetallic monomeric units of metals having a valence of +2, +3 or +4.

The above-mentioned inorganic polymers are composed of a major amount ofstannic oxide units of the formula: ##STR1## wherein at least one of thegroups R₁, R₂, R₃ and R₄ is --OH or --O-- and at least one of the groupsfrom R₁, R₂, R₃ and R₄ is an anion of a water soluble salt of tin suchas chloride, bromide, nitrate, sulfate and the like. The remainder ofthe groups R₁, R₂, R₃ and R₄ are OH, --O-- or an anion as defined above.The stannic oxide monomeric units of Formula I in a given polymer can bethe same or different. When none of the groups R₁, R₂, R₃, and R₄ are an--O-- group, the polymers which are produced are linear in nature.However, when one or more of the groups R₁, R₂, R₃ and R₄ is an --O--group, the polymer chains can crosslink with each other to produce athree dimensional polymeric structure. The polymers also contain asecond type of monomeric unit as pointed out above. These monomericunits are metal oxide monomers of the formulae: ##STR2## and mixturesthereof, wherein M₁ is a metallic ion of a metal having a valence of +2and M₂ is a metallic ion of a metal having a valence of +3. The metaloxide monomeric unit that is employed as the second monomeric unit canbe selected from the oxide of various metals which have two stablestates of oxidation in an aqueous system. The metal includes, forexample, iron, cobalt, nickel, bismuth, lead, titanium, vanadium,chromium, copper, molybdenum, antimony, tungsten, and most preferablytin.

The amount of monomeric units of Formula II or Formula III employed isnot critical.

The exact structure of the resulting polymer is not precisely known. Itis believed, however, that when a monomeric unit of Formula II is usedthat the polymer is comprised of monomeric units connected in thefollowing manner: ##STR3## When one or more of the groups R₁, R₂, R₃ andR₄ is --O--, sidechains can form and cross-linking can also occurespecially when the monomeric units of the formula ##STR4## are includedin the polymer chain. Such a polymer could have, for example, thefollowing formula: ##STR5## The letters n and n' in the above formularepresent a relatively large number, for example, 50 to 10,000.

As can be seen from the above formulae, there is a large variety ofdifferent polymeric structures which can be produced.

A highly advantageous polymer of this type is the polymer comprised ofstannic oxide and stannous oxide monomeric units. This polymer iscomprised of monomeric units of the formulae: ##STR6## The polymer isproduced in an aqueous reaction medium and is colloidal in character.Even if the water of the hydrosol is completely removed, the resultingpolymer can be redispersed by the addition of water and the product willstill be a stable colloidal dispersion of the polymer.

The polymers are prepared in the form of a hydrosol by dissolving thetin⁺ ⁴ salts in water. The +2, +3 or +4 metallic salts or finely dividedmetal is added to the aqueous mixture. The aqueous mixture is thencarefully heated up to a point somewhat below the boiling point of thereaction mixture. As the temperature increases, there will be a changein the color of the reaction mixture. This change in color is believedto be due to a rapid electron exchange between the higher valent and thelower valent ions. The color of the solution is an indication of thedegree of polymerization of the polymer with a deeper color beingindicative of a higher molecular weight. The desired molecular weight ofthe resulting polymer is dependent upon the intended end use of thepolymer as will be explained in greater detail below. After the desireddegree of polymerization has been achieved, as determined, for example,by an evaluation of the color of the reaction mixture, the reactionmixture is allowed to cool to room temperature.

The polymer can be isolated using conventional methods. However, it isgenerally not necessary for most purposes to have the polymer in theabsolute pure form. As noted above, the polymers of this invention havea strong positive charge. The residues from the reaction are, relativeto the polymer, either insoluble, electrically neutral or noncolloidal.When the polymer is applied to a negatively charged substrate, thepolymer adheres to the negatively charged substrate due to thedifference in the charges of the substrate and the polymers and possiblychemical bonding. When the substrate is washed with water, the residuesand excess amounts of polymer will be removed.

More details regarding the inorganic stannic oxide polymers may be foundin U.S. Pat. No. 3,890,429 which is incorporated by reference therein.

The inorganic stannic oxide polymers are easily deposited on a suitablesupport, preferably a polymeric support. The inorganic polymers areknown to the art to possess a high degree of adhesion for many surfaces.Thus, the methods of deposition employed can be dipping, spraying,curtain coating, roller coating, slot coating, and the like. Any excessmay be washed off with water. A relatively thin uniform layer ofinorganic polymer remains on the surface. The noble metal nucleatingsites are then generated on the inorganic polymer layer. It is notnecessary that the inorganic polymer layer be dried prior to theapplication of the noble metal compound. The thickness of the nucleatinglayer is generally in the range of 10 to 1000 A.

The noble metals may be applied to the inorganic stannic oxide polymerby a variety of methods. Preferably, an aqueous solution of a noblemetal salt or complex is applied to the inorganic polymer layer. It isbelieved that the inorganic polymer forms a reactive matrix for thenoble metal at the M⁺ ² sites where M⁺ ² is preferably Sn⁺ ².

The aforementioned coated support constitutes the image-receivingelement of the present invention and is ready for use in a silverdiffusion transfer photographic process.

In an alternative embodiment, successive coatings of the noble metalnucleating layers may be employed, in some cases separated by layers ofa suitable polymeric binder such as deacetylated chitin or gelatin. In apreferred embodiment, however, a single deposition of the silverprecipitating layer is employed.

The size of the nuclei formed are extremely small and may vary over arelatively wide range. FIGS. 1, 2 and 3 are electron micrographs. FIG. 1shows the nucleating layer at 100,000X magnification formed from thereaction product of an inorganic stannic oxide polymer (see Example Ibelow) and 0.0014M HAuCL₄. FIGS. 2 and 3 show the nucleating layer at100,000X and 300,000X magnification, respectively, formed by thereaction product of an inorganic stannic oxide polymer and 0.1M K₂PdCl₄.

When the novel image-receiving element of the present invention isemployed in silver diffusion transfer processing, the image formedtherein is characterized by a uniform mirror deposit of image silver asa result of the relatively thin nuclei layer employed. The positivesilver is more dense than that generally found in prior artimage-receiving elements and is similar in properties to that obtainedby vacuum deposited silver, which is the most compact form possible. Theabovementioned mirror can be used for printed circuits as evidenced byresistivity measurements which range from 3 to 20 ohms/cm. Theabsorption spectra is relatively neutral, i.e., similar to vacuumdeposited silver. Thus, by means of the present invention, a thin,tightly packed matrix of nuclei can be prepared so that the silverdeposited thereon is similar to vacuum deposited silver, the mostcompact form possible. FIG. 4, a transmission curve for a silver imagewhich will be described further below, illustrates the above-mentionedrelatively neutral absorption spectra.

As stated above, the method of preparing the inorganic stannic oxidepolymer is relatively simple. A metal, e.g., tin, is heated in asolution of stannic chloride and then decanted or filtered to removeexcess unreacted metal.

To apply the tin hydrosol to the support, a substrate such as a sheet ofpolyester is dipped in a solution for about 1-40 seconds, rinsed withwater, optionally dried and then dipped in a nuclei-forming solution,e.g., a 0.25 to 0.0001M solution of, for example, potassium palladoustetrachloride (K₂ PdCl₄), for about 5 to 40 seconds. It has been foundthat neither the concentration of the reactants nor the treatment timeis critical. Generally, a layer of about 0.1 to 1.0 mgs./ft.² of noblemetal is employed.

As examples of noble metal salts or complexes suitable for use in thepresent invention, mention may be made of compounds of silver, gold,palladium, platinum and rhodium. Combinations of noble metals may beused as well as single noble metals. The noble metals may be reduced onthe tin hydrosol from aqueous salts of the noble metals. Suitable noblemetal compounds include the following:

K₂ pdCl₄

PdCl₂

H₂ ptCl₆

AgNO₃

HauCl₄

(NH₄)₃ RhCl₆

The following nonlimiting example illustrates the preparation of theinorganic stannic oxide polymer hydrosol.

EXAMPLE I

To 1500 ml. of water was added 300 g. stannic chloride (SnCl₄. 5H₂ O)and 134 g. mossy tin. The solution was heated with stirring to 85° C.,allowed to cool and then decanted.

The following nonlimiting examples illustrate the preparation of theimage-receiving elements of the present invention.

EXAMPLE II

A sheet of 5 mil transparent polyester film was dipped into a 20%solution of tin hydrosol as prepared in Example I for 20 seconds. Thethus-coated sheet was then washed with distilled water an then dippedinto a solution of 0.1 molar of silver nitrate for 20 seconds. Thethusformed image-receiving element was again washed with distilledwater.

EXAMPLE III

An image-receiving element was prepared according to the procedure ofExample II except that 0.14M of HAuCl₄ was used instead of silvernitrate and the contact time of the gold solution with the inorganicstannic oxide polymer was 40 seconds.

EXAMPLE IV

An image-receiving element was prepared according to the procedure ofExample II except that 0.00014M of HAuCl₄ was used instead of silvernitrate and the contact time of the gold solution with the inorganicstannic oxide polymer was 5 seconds.

EXAMPLE V

An image-receiving element was prepared according to the procedure ofExample II except that 0.25M of K₂ PdCl₄ was used instead of silvernitrate and the contact time of the palladium solution with theinorganic stannic oxide polymer was 10 seconds.

EXAMPLE VI

An image-receiving element was prepared according to the procedure ofExample II except that 0.1M of (NH₄)₃ RhCl₆ was used instead of silvernitrate.

The image-receiving elements of the present invention are illustrated bythe results tabulated below obtained by substituting the image-receivingelements of the present invention for the image-receiving element in thePolaroid Type 107 Land film (sold by Polaroid Corporation, Cambridge,Massachusetts). The photosentive element was exposed to a conventionalstep wedge and then processed for 15 seconds. The image-receivingelements were then separated from the photosentive elements.

The maximum transmission densities of the elements are set forth below.

                  TABLE I                                                         ______________________________________                                                          Noble                                                       Image-receiving Element                                                                         Metal    D.sub.max Trans-                                      Example No.    Nuclei   mission Density                                    ______________________________________                                        II                Ag       1.45                                               III               Au       0.5                                                IV                Au       1.1                                                V                 Pd       1.15                                               VI                Rh       0.24                                               ______________________________________                                    

EXAMPLE VII

A transparent polyester film base having a coating of polyvinyl formalon one side was dipped into a 15% solution of tin hydrosol as preparedin Example I for 20 seconds, rinsed with water for 20 seconds, dippedinto a solution of 0.01M K₂ PdCl₄ for 20 seconds, then rinsed with waterfor 20 seconds and air dried. This receiving sheet was designated VII-A.

A transparent polyester film base having a coating of polyvinyl formalon one side was dipped into a 15% solution of tin hydrosol for 20seconds, rinsed with water for 20 seconds, dipped into a solution of0.01M K₂ PdCl₄ for 20 seconds, rinsed with water for 20 seconds, dippedinto the solution of tin hydrosol for 20 seconds, rinsed with water for20 seconds, dipped into the K₂ PdCl₄ solution for 20 seconds, rinsedwith water for 20 seconds and air dried. This receiving sheet wasdesignated VII-B.

The receiving units were then evaluated as a component of the Type 107film units as described above. The following results were obtained:

    ______________________________________                                                Transmission Density                                                          (D.sub.max)      Tone                                                 ______________________________________                                        VII-A     0.62               black-green                                      VII-B     1.32               neutral                                          ______________________________________                                    

It has also been found that one or more additional metals may beemployed in conjunction with the noble metal. The additional metal maybe noble or non-noble.

The following table illustrates the results obtained with varioussystems within the scope of the present invention. Receiving elementswere prepared by dipping a transparent polyester film base in a 20%solution of the tin hydrosol of Example I for 20 seconds, rinsed withwater for 20 seconds, dipped into a solution of K₂ PdCl₄ for 20 seconds,rinsed for 20 seconds with water, dipped into a solution of a salt ofthe second metal for 20 seconds, rinsed with water for 20 seconds andair dried. The thusformed image-receiving elements were processed asabove in a Type 107 format. The results are set forth in the table.

                                      TABLE 2                                     __________________________________________________________________________                          Transmission Density                                    Noble Metal/Additional metal                                                                        Neutral                                                                            Red  Green                                                                              Blue  Tone                               __________________________________________________________________________    0.1M K.sub.2 PdCl.sub.4 /Cu*                                                                        .60  .55  .63  .65  blue-black                          0.1M K.sub.2 PdCl.sub.4 /0.1M Cu(NO.sub.3).sub.2                                                    .57  .47  .61  .63  blue-black                          .01M K.sub.2 PdCl.sub.4 /0.01M Cu(NO.sub.3).sub.2                                                   .57  .53  .57  .60  blue                                .01M K.sub.2 PdCl.sub.4 /0.1M Copper acetate                                                        .79  .73  .80  .74  purple-black                        0.01M K.sub.2 PdCl.sub.4 /0.01M Copper acetate                                                      .64  .57  .69  .71  purple-black                        0.01M K.sub.2 PdCl.sub.4 /0.01M Co(NO.sub.3).sub.2                                                  .65  .61  .67  .63  purple                              0.01M K.sub.2 PdCl.sub.4 /0.1M Co(NO.sub.3).sub.2                                                   .53  .47  .57  .59  blue-black                          0.01M K.sub.2 PdCl.sub.4/0.0014 M HauCl.sub.3                                                       .99  1.01 .97  1.11 green                               0.01M K.sub.2 PdCl.sub.4 /0.1M NiCl                                                                 .93  .90  .96  1.12 black                               0.01M K.sub.2 PdCl.sub.4 /0.0014M HAuCl.sub.4 /0.1M AgNO.sub.3                                      1.22 1.15 1.25 1.40 black                               0.01M K.sub.2 PdCl.sub.4 /0.1M TiO(SO.sub.4)                                                        .38  1.02 .90  1.05 green                               0.01M K.sub.2 PdCl.sub.4 /0.01 M VO(SO.sub.4)                                                       .50  .65  .70  .94  green                               0.01M K.sub.2 PdCl.sub. 4 /0.1M VO(SO.sub.4)                                                        1.11 1.13 1.17 1.25 blue                                0.01M K.sub.2 PdCl.sub.4 /0.01M Ni(SO.sub.4)                                                        1.00 1.12 1.18 1.30 purple-black                                              .56  .60  .55  .58  green-black                         0.01M K.sub.2 PdCl.sub.4 /0.1M Ni(SO).sub.4                                                         .63  .57  .68  .72  brown                               0.01M K.sub.2 PdCl.sub.4 10.01M Cu(SO.sub.4)                                                        .55  .57  .56  .58  green-black                         0.01M K.sub.2 PdCl.sub.4 /0.1M Cu(SO.sub.4)                                                         .60  .64  .62  .65  brown-black                         0.005M K.sub.2 PdCl.sub.4 /0.0007M HAuCl.sub.4                                                      1.14 1.15 1.14 1.17                                     0.0010M K.sub.2 PdCl.sub.4 /0.0014M HAuCl.sub.4                                                     1.45 1.47 1.38 1.29                                     __________________________________________________________________________    *The copper was provided by mixing the following solutions:                   A.  CuSO.sub.4 . 5H.sub.2 O                                                                      10 gms.                                                        Formaldehyde (37%)                                                                           60 mls.                                                        Methanol      300 mls.                                                        Distilled water                                                                             to make 1 liter                                             B.  Sodium hyroxide (50%)                                                                        80 gms.                                                        Potassium-sodium tartrate                                                                    28 gms.                                                        Distilled water                                                                             to make 1 liter                                             __________________________________________________________________________

The following nonlimiting example illustrates the utility of the novelimage-receiving elements of the present invention in an integral filmunit of the aforementioned type.

EXAMPLE VIII

A film unit was prepared comprising a transparent polyester film basecarrying on one surface an additive color screen of approximately 1000triplet sets per inch of red, blue and green filter screen elements inrepetitive side-by-side relationship; a protective overcoat comprising alayer of a polyvinylidine chloride copolymer and a layer of polyvinylbutyral; a nucleating layer of the inorganic stannic oxide polymerhaving palladium reduced thereon prepared by coating the polyvinylbutyral layer with the inorganic stannic oxide polymer of Example I andthen contacting the inorganic polymer layer with 0.01M potassiumpalladous tetrachloride by immersion for 30 seconds; a panchromaticallysensitized hardened gelatino silver iodochlorobromide emulsion coated ata coverage of about 115 mgs./ft.² of gelatin and about 100 mgs./ft.² ofsilver with about 7.18 mgs./ft.² propylene glycol alginate and about0.45 mg./ft.² of sodium dioctyl sulfosuccinate; and an antihalation topcoat comprising about 220 mgs./ft.² of gelatin, about 5.7 mgs./ft.² of asilver salt of a dye of the formula: ##STR7## about 0.380 mg./ft.² of acommercial dispersing agent (Daxad 11 sold by W. R. Grace and Company,Cambridge, Massachusetts); about 0.847 mg./ft.² of a commercialsurfactant sold by Rohm & Haas Company, Philadelphia, Pennsylvania underthe trade name Triton X-100; about 18.01 mgs./ft.² of goldmercaptobenzimidazole. The above-described antihalation topcoat isdisclosed and claimed in copending application Ser. No. 383,261 filedJuly 27, 1973.

The above-described film unit was exposed to a conventional step wedgeand was developed by contacting the film unit for about 60 seconds witha processing composition comprising:

    ______________________________________                                        Sodium hydroxide     1763       g.                                            Hydroxyethyl cellulose                                                        (high viscosity)     150        g.                                            Tetramethyl reductic acid                                                                          2775       g.                                            Sodium sulfite       199        g.                                            N-benzyl-α-picolinium bromide                                                                198.75     g.                                            Sodium thiosulfate   308.3      g.                                            Water                16894      cc.                                           ______________________________________                                    

Characteristic curves, reproduced herein as FIG. 5, were prepared byplotting the neutral column density to white light and to the red, greenand blue light as a function of exposure D_(max) transmission density of˜ 3.0 to white light and a D_(min) of ˜ 0.3 to white light weremeasured. The image showed quite neutral tone and the image silver washighly compact. The curve in FIG. 4 was obtained on a film unit similarto that described in Example VIII processed in the same manner and withthe same processing composition, and illustrates the neutral tone of theimage.

To illustrate the relatively thin receiving layer obtainable by means ofthe present invention as well as the compact, dense positive silverimage obtainable by diffusion transfer processing, reference may be madeto FIGS. 6 through 11.

FIG. 6 is an electron micrograph of 100,000 magnification of a crosssection of a film unit prepared according to the procedure of ExampleVIII wherein 11 is the protective overcoat, 13 is the nucleating layerand 15 is the emulsion layer.

FIG. 7 shows the film unit of FIG. 6 after processing wherein thepositive silver image 14 has been deposited in the receiving layer. Thedense, compact silver layer can be seen.

FIG. 8 is a top view of 40,000 magnification of the positive silverimage 14 of FIG. 7 with the top coat and emulsion removed. The densenessof the silver packing is evident.

For comparison, film units were prepared using a prior art coppersulfide nucleating layer and are shown in FIGS. 9, 10 and 11. FIG. 9 isa prior art film unit showing protective overcoat 11, nucleating layer21 carrying copper sulfide nuclei in a polymeric binder and emulsionlayer 15. It will be noted that the prior art nucleating layer is 3 to 4times as thick as the receiving layer of the present invention. FIGS. 10and 11, which correspond to FIGS. 7 and 8, respectively, do not show thecompact, dense positive silver deposition achieved in the presentinvention as illustrated in FIGS. 10 and 11.

The support employed in the present invention is not critical. Thesupport or film base employed may comprise any of the various types oftransparent rigid or flexible supports, for example, glass, polymericfilms of both the synthetic type and those derived from naturallyoccurring products, etc. Especially suitable materials, however,comprise flexible transparent synthetic polymers such as polymethacrylicacid, methyl and ethyl esters; vinyl chloride polymers; polyvinylacetals; polyamides such as nylon; polyesters such as the polymericfilms derived from ethylene glycol terephthalic acid; polymericcellulose derivatives such as cellulose acetate, triacetate, nitrate,propionate, butyrate, acetate-butyrate; or acetate propionate;polycarbonates; polystyrenes; and the like.

The adhesion of tin hydrosols to various negatively charged surfaces iswell known and thus subcoats and surface treatments such as coronadischarge are generally not required.

What is claimed is:
 1. A photographic image-receiving element for use insilver diffusion transfer processes which comprises a support carrying alayer of an inorganic stannic oxide polymer hydrosol, said polymerhaving a noble metal reduced thereon, wherein said inorganic stannicoxide polymer hydrosol comprises stannic oxide monomeric units andmetallic oxide monomeric units of a metal having a valence of +2 or +3.2. A product as defined in claim 1 wherein said polymer is comprised ofstannic oxide units of the formula: ##STR8## wherein at least one of thegroups R₁, R₂, R₃ and R₄ is --OH or --O-- and at least one of the groupsR₁, R₂, R₃ and R₄ is an anion of a water soluble salt of tin and theremainder of the groups R₁, R₂, R₃ and R₄ are --OH,-- O-- or an anion ofa water-soluble salt of tin and wherein said polymer contains a secondtype of monomeric unit selected from the group consisting of metal oxidemonomers of the formulae: ##STR9## and mixtures thereof, wherein M₁ is ametallic ion of a metal having a valence of +2 and M₂ is a metallic ionof a metal having a valence of +3.
 3. A product as defined in claim 2wherein said metallic ions M₁ and M₂ are selected from the groupconsisting of iron, cobalt, nickel, bismuth, lead, titanium, vanadium,chromium, copper, molybdenum, antimony, tungsten and tin.
 4. The productas defined in claim 1 wherein said noble metal is selected from thegroup consisting of gold, platinum, palladium, silver, rhodium, andcombinations thereof.
 5. The product as defined in claim 1 whichincludes a second metal reduced on said polymer.
 6. The product asdefined in claim 4 wherein said noble metal is palladium.
 7. The productas defined in claim 1 which includes a photosensitive silver halideemulsion layer associated therewith.
 8. The product as defined in claim7 wherein said image-receiving element and said emulsion layer arecoated on the same support.
 9. In a silver diffusion transfer process,the steps which comprise developing an exposed photographic silverhalide emulsion with a diffusion transfer processing composition,forming an imagewise distribtuion of soluble silver complex as afunction of the point-to-point degree of exposure thereof, andtransferring, by imbibition, at least part of said imagewisedistribtuion of said soluble silver complex to a superposedimage-receiving layer to thereby provide a silver transfer image to saidimage-receiving layer, the improvement wherein said image-receivinglayer comprises a support carrying a layer of inorganic stannic oxidepolymer hydrosol, said polymer having a noble metal reduced thereon,wherein said inorganic stannic oxide polymer hydrosol comprises stannicoxide monomeric units and metallic oxide monomeric units of a metalhaving a valence of +2 and +3.
 10. A process as defined in claim 9wherein said polymer is comprised of a major amount of stannic oxideunits of the formula: ##STR10## wherein at least one of the groups R₁,R₂, R₃ and R₄ is --OH or --O-- and at least one of the groups R₁, R₂, R₃and R₄ is an anion of a water soluble salt of tin and the remainder ofthe groups of R₁, R₂, R₃ and R₄ are OH, --O-- or an anion of a watersoluble salt of tin and wherein said polymer contains a second type ofmonomeric unit selected from the group consisting of metal oxidemonomers of the formulae: ##STR11## and mixtures thereof, wherein M₁ isa metallic ion of a metal having a valence of +2 and M₂ is a metallicion of a metal having a valence of +3.
 11. A process as defined in claim10 wherein said metallic ions M₁ and M₂ are selected from the groupconsisting of iron, cobalt, nickel, bismuth, lead, titanium, vanadium,chromium, copper, molybdenum, antimony, tungsten and tin.
 12. A processas defined in claim 9 wherein said noble metal is selected from thegroup consisting of gold, platinum, palladium, silver, rhodium andcombinations thereof.
 13. A process as defined in claim 9 which includesa second metal reduced on said polymer.
 14. A process as defined inclaim 12 wherein said noble metal is palladium.
 15. A photographicelement comprising a support carrying a layer of an inorganic stannicoxide polymer hydrosol thereon, said polymer having a substantiallyuniform layer of a noble metal reduced thereon, said element furtherincluding an imagewise distribution of silver on said layer saidinorganic stannic oxide polymer hydrosol comprising stannic oxidemonomeric units and metallic oxide monomeric units of a metal having avalence of +2 or +3.
 16. A photographic film unit which comprises atransparent support carrying, in order, an additive multi-color screen,a silver precipitating nuclei layer and a layer comprisingphotosensitive silver halide crystals, wherein said silver precipitatinglayer comprises a layer of an inorganic stannic oxide polymer hydrosol,said polymer having a noble metal reduced thereon said inorganic stannicoxide polymer hydrosol comprising stannic oxide monomeric units andmetallic oxide monomeric units of a metal having a valence of +2 or +3.17. A film unit as defined in claim 16 which includes a substantiallyprocessing composition permeable polymeric layer intermediate saidsilver precipitating layer and said layer comprising photosensitivesilver halide crystals.
 18. A film unit as defined in claim 16 whereinsaid photosensitive silver halide layer has a silver coverage of notmore than about 200 mgs./ft.².
 19. A film unit as defined in claim 16wherein said screen is a trichromatic screen possessing red, green andblue optical filter elements.
 20. A product as defined in claim 16wherein said polymer is comprised of stannic oxide units of the formula:##STR12## wherein at least one of the groups R₁, R₂, R₃ and R₄ is --OHor --O-- and at least one of the groups R₁, R₂, R₃ and R₄ is an anion ofa water soluble salt of tin and the remainder of the groups R₁, R₂, R₃and R₄ are --OH, --O-- or an anion of a water soluble salt of tin andwherein said polymer contains a second type of monomeric unit selectedfrom the group consisting of metal oxide monomers of the formulae:##STR13## and mixtures thereof, wherein M₁ is a metallic ion of a metalhaving a valence of +2 and M₂ is a metallic ion of a metal having avalence of +3.
 21. A product as defined in claim 20 wherein saidmetallic ions M₁ and M₂ are selected from the group consisting of iron,cobalt, nickel, bismuth, lead, titanium, vanadium, chromium, copper,molybdenum, antimony, tungsten and tin.
 22. The product as defined inclaim 16 wherein said noble metal is selected from the group consistingof gold, platinum, palladium, silver, rhodium, and combinations thereof.23. A photographic process which comprises, in combination, the stepsof:(a) exposing to incident actinic radiation a photographic film unitcomprising, in order, a transparent support carrying an additivemulticolor screen comprising red, green and blue optical filter elementsin a screen pattern, a silver precipitating layer, a substantiallyprocessing composition permeable polymeric layer, a layer comprisingphotosensitive silver halide, said silver precipitating layer comprisingan inorganic stannic oxide polymer hydrosol having a noble metal reducedthereon said inorganic stannic oxide polymer comprising stannic oxidemonomeric units and metallic oxide monomeric units of a metal having avalence of +2 or +3; and (b) contacting the exposed element with aprocessing composition comprising a silver halide solvent and a silverhalide developing agent to thereby provide to the element a silvertransfer image in terms of the unexposed areas of said silver halidelayer, as a function of the point-to-point degree of exposure thereof;said silver transfer image being viewable without separation of saidsilver precipitating layer and said silver halide layer.